Inductive heating apparatus



y 1945' H. A. STRICKLAND, JR 2,400,660

INDUCTIVE HEATING APPARATUS Filed 001.. 13, 1943 mmi! 4- 3 v INVENTOR Harold H. s gticklandk ATTORNEY Patented May 21, 1946 INDUCTIVE HEATING APPARATUS Harold A. Strickland, Jr., Detroit, Mich, assignor, by mesne assignments, to Budd Wheel Company, a corporation of Pennsylvania Application October 13, 1943, Serial No. 506,018

. 6 Claims. (01. 219-13) This invention relates to inductive heating apparatus and particularly to such apparatus as will insure uniform heating of a charge or bar throughout its entire length.

In my copending application filed September 2, 1943, I have disclosed an in duction furnace having particular adaptation for the heat treatment of bars of excessive length. Frequently in the use of the furnace of this copending application, it is desirable to insert one-- half of the workpiece within the heating cham- Serial No. 500,963,-

her and subject it to the necessary temperatures and subsequent mechanical modificationasuch as to a shell form, and subsequently insert the untreated other half of the workpiece for a similar heat treatment and mechanical modification. In carrying out the second step of this operation, however, complete insertion of the second half usually preventedfrom the fact that the modified end of the workpiece is enlarged beyond the furnace chamber diameter, thus preventing com-- ltis, accordingly, a primary object oi the present invention to provide apparatus which will permit heating of a workpiece at the charge opening or mouth of the heating chamber at points adjacent and, if desired, external to the plane, including the outer end of the heating coil. Another object of the invention is to facilitate ,inanufacture of completely formed articles on ed on an inner lining of mica sheets ll of the workpiece into th heating chamber is either end of a single workpiece without separation oi the workpiece at an intermediate point.

An object also following from the previously mentioned objects is to'insure' uniformity of heatin in a workpiece throughout the heating chamber of aninduction heating coil. Still another object is to provide means for forcing the magnetic flux developing from the application of alternatin current to an inductive heating coil toward the axis of the coil adjacent the end thereof. Other objects, such as relate to detailed construction,

.will appear on considerationof the embodiment of the invention hereinafter described and illustrated in the accompanying drawing, in which:

position by supporting ribs or Figure 2. c

The induction furnace as shown in Figure 1 is in general similar to that shown in my copending application Serial No. 384,503 filed Marchv2l, 1941, and includes a coil l0 of a tubular copper conductor which is rectangular in cross section so as to facilitate close placement of the turns each in relation to the other. The coil is mountwhich in turn overlie the supporting brickwork 12 held in end plates as shown in my copending application hereinabove referred to. i I

Overlying the heating coil is is an outer layer it of insulation preferably having an asbestos base. The extreme outer end of the heating coil contacting with the outer turn thereof is formed of a plurality of annular insulation plates terminating in a thicker annular strip it forming the end piece of the furnace coil. The mica casing ii, brick structure 62, and exterior casing it are all extended so as to terminate in the plane including the end annular insulation strip 68. The supporting mechanism for the heating coil may be of any desired form, such as for example shown in my copending application Seriai'lt'o. 384,503 and is not shown because it forms no part of the invention. The end or the heating coil with its enclosed heating chamber H as shown in Figure 1 is adjacent the mouth, inlet, or charge opening of the furnace.

A section E8 of the front. plate of the furnace casing is illustrated in Figure l, the same having a charge opening in which is placed the mouthpiece is of the heating chamber. 'this monthpiece consists of a non-magnetic metal plate having a flat base forming the outer surface.

and extending inwardly a plurality of integral approximately the same as the adjacent inner surface or the heating chamber I? o! the furnace.

With the construction as described, when a long workpiece, such as the cylindrical bar 22, is inserted within the heating chamber before any modification oi the structure thereof, fiux and consequent eddy currents in the workpiece appear with substantial uniformity throughout the bar length within the region defined by the inner and outer turns of the heating coil. The

'to the fact that because of the increased diameter oi the section 23 inward movement of the reversed workpiece unit is limited by the inwardly directed finger ends 2| of the furnace mouth, the section 23 coming into contact with these fingers at a point where the outer end oi section 24 is substantially outside the efiective heating range of the outer coil turns. Consequently, when the heating current is turned on, the fiux coupling with the outermost part of bar section 24 will be enough less than that toward the inner part of the section that a lesser degree of heating results at that end.

The means employed to overcome this difiiculty consists in a series of bars of laminated iron plates 26 forming a broken bar ring, as

shown particularly in Figures 2 and 3, which" are placed between the ends 2| of the'iurnace mouth fingers and extent radially outwardin a transverse plane with the surface of each plate parallel to the coil axis. In order to'hold these plates in position, the bases thereoi are brazed on the side away from the coilto or clamped between the finger terminals.

With this laminated construction as shown, there is provided a magnetic path which traverses a greater bar length but which is of lower magnetic reluctance than the path through air alone. As a consequence, the coil fiux traverses the laminated structure instead of taking a shorter distance leakage path of greater reluctance. In this way the density of flux ad- Jacent the area of the front end or the work piece section 24 is maintained to such an extent that adequate heating is imparted thereto for a greater distance and satisfactory mechanical modification oi the metal structure is accordingly made possible;

Advantages of the construction additional to that mentioned include the shielding action of the i'erro-magnetic bar ring for the guide fingers; which without the ring, would absorb undesirably a substantial amountof stray energy from the fiux field.

I have shown a form of my invention which may be preferred butit is obvious that modifications in the details entering into the structure may be made, and hence I do not desire to be 2,400,660 low ring having, in inner contour, a diameter limited to the disclosed embodiment except as may be required by the scope of the claims hereto appended.

What is claimed is:

1. In inductive heating apparatus, a tubular induction heating coil Iorming a heating chamber adapted to receive a workpiece, a casing having a charge opening for said chamber, guide fingers of non-magnetic metallic material between said charge opening and chamber forming a constricted opening, and means for increasing the inductive fiux density in the charge opening external to the heating chamber adjacent the axis thereoi, said means comprising ferro-magnetic bars attached to and between said fingers.

2. In inductive heating apparatus, a tubular induction heating coil forming a heating chamber having an inlet opening, a. casing having a charge opening'for said chamber, non-magnetic metal guide means between said chamber and charge opening for guiding a workpiece into said chamber, and additional means secured to said guide means between the coil and guide means for directing the coil end flux toward the coil axis whereby the eiIective coil heating zone is extended centrally and outwardly of the coil opening and stray flux is reduced;

3. In inductive heating apparatus, a tubular induction heating coil forming a heating chamber, a casing having a charge opening for said chamber, guide fingers of non-magnetic metallic material between said casing and chamber adjacent said charge opening, and means including radial magnetic members secured to the inner ends of said guide fingers between the guide fingers and coil for spreading coil fiux toward the coil axis adjacent the finger ends.

4. In inductive heating apparatus, a tubular induction heating coil forming a heating chamber, a casing having a charge opening for said chamber, radially extending circumierentially laminated term-magnetic plates positioned adjacent the end of said chamber between the chamber and charge opening and forming a broken ring therebetween and a non-magnetic metal support for said ring extending therefrom to the casing.

5. In inductive heating apparatus, a tubular induction heating coil forming a heating chamber having a charge opening, a non-magnetic metal workpiece guide adjacent said opening and means at the, charge opening including radially extending magnetic material plates attached to said guide tor centering the magnetic fiux of said coil toward the coilaxis .and shielding the guide from stray fiux.

6. A workpiece guide for coil induction furnaces comprising an annular metal base adapted for positioning adjacent the inlet opening of the coil chamber, non-magnetic metal fingers attached to said base and converging toward said coil inlet and means for shielding the fingers from the stray magnetic flux, said means comprising plural coplanar bars 01' i'erro-magnetic metal attached to the finger tips.

HAROLD A. STRICKLAND, J R. 

